Chromium (Cr) and its compounds are the basic raw materials commonly used in metallurgy, metal processing, electroplating, tanning, paint, pigments and other industries. In the production process of the above-mentioned industries, a large amount of chromium-containing waste gas, waste water and waste residue are generated, which causes serious environmental contamination problems. Since Cr(VI) is a heavy metal that is soluble in water, and the site contaminated by Cr(VI) can be as deep as 100 meters sometimes, and how to remediate such chromium-containing soil which is heavily contaminated has always been a problem in the environmental protection field.
Although there are many treatment methods, most of them have various problems. At present, the mainstream process for treating chromium-containing soil is to reduce hexavalent chromium by using ferrous sulfate. However, ferrous sulfate is low in pH, corrosive, and is easily oxidized and deactivated in the air. Moreover, ferrous iron is easily adsorbed and intercepted by soil and has poor permeability. Therefore, the reduction of hexavalent chromium can only be short-term rather than permanent. In order to effectively treat chromium-containing soil, it is often necessary to add an excess of ferrous sulfate, which in turn tends to cause secondary pollution of sulfate radical. Patent No. 201410101586.0 describes an in situ remediation method for a Cr(VI)-containing site using ferrous sulfate. Since ferrous iron is easily oxidized and deactivated in air, the method uses citric acid with a low pH to inhibit its oxidation and increase its permeation, but correspondingly increases the cost and acidifies the soil while still causing secondary pollution of sulfate. Patent No. 201310642919.6 describes an situ remediation method for a Cr(VI)-containing site using organic waste, which is a method for treating a site contaminated with hexavalent chromium at a low cost. However, this method may easily cause the microbial agent to be intercepted in a certain section of the soil through natural permeation, which causes the microbial agent to be unable to be transported, and the organic matter and the dissolved hexavalent chromium solution are permeated into the underground water, causing secondary contamination of the underground water.
In general, for the site contaminated with a high concentration of hexavalent chromium, traditional chemical reagents are difficult to reduce all the hexavalent chromium, and the microorganism reducing microbial agents are easily killed by high-concentration hexavalent chromium to be ineffective.